I. Field of the Invention
The present invention relates generally to a valve for controlling the passage of fluids. In particular, the present invention relates to an elastomer body which is installed in a main valve body and which can be stretched to control the fluid flow between two points.
II. Background and Description of Related Art
In biochemistry and biotechnology research, the precise metering of fluids is critical to the success or failure of experiments and/or the production of bioengineered products. Many existing valve designs are simply inappropriate for such use. Valves which are suited for such use, however, are those having designs which use elastomeric components, because of their resilient spring qualities. Elastomeric elements are especially well suited for the design of valves which are to be used to precisely control the flow rate of a fluid or to dispense a precise volume of fluid. Some valves, however, are designed to merely open or close an opening, without regard to the flow rate or output volume of fluid allowed by the valve. Such designs do not take into account precision fluid flow control. For example, U.S. Pat. No. 3,584,834 to Reid et al. discloses a valve assembly that features a rubber element that acts as both a stopper for the valve and as a spring. When a button is depressed, the stopper moves and the valve opens. When pressure on the button is released, the spring properties of the rubber element draw the stopper back into place. The stopper valve design is not directed to the precision control of fluid flow.
Other valves are designed to select among influents to be passed to an output port. For example, U.S. Pat. No. 4,275,765 to Dugas discloses a valve assembly utilizing an elastomeric member that is designed to enable a fast flush of body fluids from either of two catheters to a pressure transducer. The elastomer member has a cylindrical cavity into which a plunger is inserted. Pushing the plunger distorts the elastomeric member, allowing the fast flush of fluids. Again, the valve is not suitable for precise fluid flow control between ports, and fluid remains in the valve cavity even when the valve is closed. Thus, the valve itself must be flushed out if different ports are connected to it between uses and precision of flow is limited by the amount of fluid left in the is valve cavity when the valve is closed. In a precision valve, this unswept or dead volume must be minimized.
When the influent to a device is not pressurized, a valve is sometimes needed so that the influent may be drawn into a container and then passed along to an output port. For example, U.S. Pat. No. 2,888,034 to Clegg discloses a valve assembly utilizing a high density rubber piece as a valve element. The valve assembly includes an inlet port, an outlet port, and an intermediate chamber. A piston plunger causes a vacuum condition in the intermediate chamber, and the valve element allows fluid to flow from the inlet port into the intermediate chamber. The piston plunger then applies a pressure stroke and the valve allows fluid in the intermediate chamber to flow to the outlet port. Precision control of fluid flow from inlet port to outlet port is not provided by this two stroke valve.
In some applications, however, precise control of the flow of a pressurized fluid from an input port to an output port is necessary. For example, in chemical applications, minute quantities of particular fluids are frequently needed in forming compounds. In other cases, while the quantity required is not minute, the quantity that is provided must be precisely dispensed. In pharmaceutical applications, drug manufacturers require precise control of the volume of components making up the drug. In other medical applications, for example surgery, control of bodily fluid flow or of anesthetics is critical. Precise control of fluid flow rates is desirable in agricultural, aerospace, and other commercial applications as well.
Other known valves also use elastomer members. For example, U.S. Pat. No. 3,548,878 to Brigandi discloses a valve assembly utilizing a bellows type expansion plug formed out of a resilient material such as rubber. The pleats of the bellows provide resilient sealing points along the internal walls of the valve housing when the bellows is compressed. When a plunger causes the bellows to expand, fluid is allowed through the valve from an inlet port to an outlet port. A clear path is never made for fluid flow; fluid pressure must overcome the sealing force of the pleats for the fluid to flow. As the bellows expands, the sealing force of the pleats becomes weaker and easier to overcome by the fluid force. Fluid flow therefore becomes greater as the bellows is expanded.
For truly precise control of fluid flow, however, the pressure of the influent should not be relied upon to overcome the sealing force of the valve. A clear path for the fluid should be provided when the valve is in the open position. The elastomeric qualities of the valve element should not be solely relied upon to return the valve to the closed position. Such reliance can cause the valve element to wear out prematurely, and would certainly make the element less reliable over the lifetime of the valve. Rather, the valve should be equipped with a spring which returns the valve to the closed position and which counteracts fluid pressure forces which would otherwise tend to open the valve.
Some valves are known to use springs to close the valve. For example, U.S. Pat. No. 2,095,770 to Sorensen discloses a valve assembly that utilizes a coil spring. The force of the spring must be overcome in order to open the valve. However, the spring is the valve element itself; it is not used to return an elastomeric valve element.